Radio direction finder



Aung. 27, 1946.

F'.l c. sANDRl-:TTO ET AL RADIO DIRECTION FINDER -Filed Jn. 12, 1942 3 Sheets-Sheet 1 I SQQS 1 -II NN Aug. 27, 1946.

P. c. sANpRETTo ET A1. 2,406,637

RADIO' DIRECTION FINDER Filed Jan. 12, 1942 3 Sheets-Sheet 2 P. c. sANDRETTo ET Ax. 2,406,637

Aug. 27, 1946.

RADIO DIRECTION FINDER 3 Sheets-Sheet 3 Filed Jan; l2, 1942 Mxm,

fyag y Patented Aug. 27, 1946 UNITED STATES PATENT FFCE 2,406,637 RADO DIRECTION FINDER Application raneaiy 12, 1942, 'serial No. 426,372

thai, Brookfield, lill.,

The present application is a continuation in part of our copending application Serial No. 403,802, led July 24, 1941, and entitled Radio direction finder.

The invention relates to control systems for radio direction finders, more particularly to direction finders of the type disclosed in our said copending application and control means therefor, and the invention has for an object the pro- Vision of reliable and accurately controlled direction finders cf this character.

In various types of direction finders, and particularly those having relatively large rotating antenna means such as are disclosed in cur said prior application, it is necessary or desirable that the antenna structure and the receiver unit be located in a relatively open area of large size which is free from power lines, metal fences, and similar structures which might iniluence the accuracy of the bearings received. It is also desirable that the necessity for an attendant at the site of the antenna structure be eliminated7 and that the operator of the direction nder equipment be stationed in a readily accessible cfce or control station remote from the antenna site.

In receiving and recording the bearing records obtained through proper manipulation of the antenna structure and in controlling these manipulations, it is of course necessary to transmit between the antenna structure and the remote control station not only the incoming signals for producing the bearing record, but also a plurality of outgoing signals, and it is of course undesirable to utilize separate control wires for each control or bearing signal. Accordingly, it is a further object of this invention to provide an automatically controlled radio direction finder and a remote control system therefor, wherein a single transmission line is employed to carry the various control signals between the antenna site and the remote control station.

In carrying out the invention in one form, we provide at the antenna site or eld station an antenna structure adapted to be selectively connected in a plurality of circuit arrangements to provide bearing signals of different character, means for controlling the circuit connections of the antenna structure, and a plurality of radio frequency receivers adapted selectively to be oonnected to the antenna structure. In addition, there is provided at the eld station a source of relatively low signal frequency controlled by indexing means associated with the antenna structure, and a motor for suitably rotating the antenna structure at the desired speed. The varie.

9 Claims. (Cl. Z50-11) ous output circuits from the radio frequency receivers and the source of low frequency signaling energy are arranged to be impressed on a single transmission line which leads to the control station. At the control station suitable selective iter means are provided for separating the various frequencies transmitted from the eld station and conducting these separated frequencies to corresponding recording and indicating means. In addition, the control station is provided with a plurality of signal transmitting means for selectively imposing on the transmission line, signal frequency currents of either continuous or intermittent character for selectively controlling at the antenna site the operating motor, the antenna connections, and the respective radio frequency receivers so as to effect the desired operation of the direction finder system.

For a more complete understanding of the invention, reference should now be had tothe draw ings in which:

Figs. 1 and 2 are respectively the leftand right-hand sides ofl a single circuit diagram illustrating a remote control system and direction finder embodying the present invention;

Figs. 3 and 4 are, respectively, circuit diagrams illustrating the detailed circuit connections of the selector control and cardioid control means illustrated generally in Fig. l; and

Fig. 5 is a diagrammatic illustration of one of the radio frequency receivers.

Referring now to the drawings, Fig. 1 illustrates somewhat diagrammatically the antenna structure and related equipment which comprise the eld station located at the antenna site. The antenna structure is shown as comprising a pair of spaced apart shielded loop antennas il) and Il, which are preferably, as described in our above referred to copending application, mounted in face-to-face relation on the opposite ends of a horizontally extending support or beam l2 which is carried on the upper end of a rotatable post i3 mounted on a suitable base l5 containing a driving motor and suitable gearing (not shown) for rotating the post and the antenna structure at a predetermined constant speed. Intermediate the loop antennas IE! and H is a vertical antenna I4 mounted on substantially the laxis of rotation of the post I3.

As is more fully explained in our copending application, the loops l0 and Il are intended selectively to be connected in opposed parallel relation with each other, so that either two or four hulls will be produced in the signal output of the receiver to which the loops are connected, de-

3 pending upon the characteristics of the propagating medium and the received radio wave, or one or both of the loops may be connected in circuit with the Vertical antenna I4 so that the output signal of the receiver will follow the usual cardioid pattern for the purpose of indicating which of the previously referred to nulls represents the true bearing of the transmitting station.

In order to provide for such selective connection of the loops I and II and the antenna I4, a switching means, which is illustrated as a relay I6, is provided having a plurality of stationary contacts I1, I8, I9, 20, and 2|, and co-operating movable contacts 22, 23, and 24. It will'be observed that when the relay I6 is in the deenergized position shown in the drawings, the loops I0 and II will be connected in opposed parallel circuit relation with each other to a pair of conductors or bus bars 25 through the relay contacts I1, 22, I9, and 23. Upon energization of the relay I6, these contacts will open and the two loops I0 and II will be connected in additive parallel relation with each other to the conductors 25 through relay contacts I8, 22, 20, and 23, the vertical antenna at the same time being connected to a third bus bar 26 through the relay contacts 24 and 2|. The manner in which the cardioid relay I6 is selectively energized, so as to produce a cardioid pattern during one revolution of the antenna structure and thereafter to connect the loops I0 and II in opposed parallel relation during subsequent revolutions, will be Y more fully described hereinafter. v

Associated with the antenna structure and adapted selectively to be connected to the bus bars 25 and 25, are a plurality of radio frequency receivers 2'! to 30, inclusive. each of which is tuned to one of the various frequencies on which the direction finder is to be used.` suitable multiple pole switches 3| to 34V being provided for effecting the desired connection of the receivers to the bus bars. While four radio receivers are shown, it rwill of course be understood that any desired number may be provided, within the limits of the selector switch and the signaling means to be hereinafter described for selectively operating switches 3| to 34, inclusive.

While the radio frequency receivers may beof any desired type, they are preferably of the type described with particularity in our above referred to copending application, wherein a pair of beat oscillators are arranged to beat with the carrier of the signal frequency to provide a c-o-nstant audio output beatnote regardlessV of variations in the carrier frequency. In Fig. the receiver 2'! is shown somewhat diagrammatically as including a converter tube IBI having a plurality of control electrodes |02, |03 and |04, the control electrode |04 being supplied withthe carrier frequency through the radio frequency stage (not shown) of the receiver, and the control electrodes |03 and |02 being respectively connected as shown to suitable crystal oscillators 35 and 35. 'I'he oscillators 35 and 35 are arranged to produce xed frequencies having a frequency difference equal to the frequency which the band pass filter 54 (Fig. 2) is designed to pass.

For example, if the band pass filter is designed to pass a frequency of 1020 cycles plus or minus 30, the frequencies of the oscillators 35 and 35 will be so selected as to have a frequency difference equal to 1020 cycles. When the frequencies of the two crystal oscillators and the carrier are impressed on the control electrodes of the converter tube IOI, two beat frequencies will be 4 generated equal respectively to the difference `between the carrier frequency and the frequency of oscillator 35, and to the difference between the carrier frequency and the frequency of oscillator 36. These two beat frequencies pass through the intermediate frequency amplifier 3l which preferably is of the type having a Wide response curve, and in the second detector contained in the detector and audio amplifier 38 these two intermediate frequencies beat together to form a beat note having a frequency equal to the difference between the xed frequencies of the two oscillators.

Y It will of course be understood that similar oscillators having an identical frequency separation are associated with each of the radio frequency receivers 23, 29, and 30, as shown in Fig. 1. The arrangement i-s such that a constant beat note equal to the frequency separation of the two oscillators, which may be, for example, a frequency of 1020 cycles, will be produced at the output of the audio amplifier regardless of the respective frequencies of the carriers to which the various radio frequency receivers are tuned.

Also associated with the antenna structure at the field station is aV suitable indexing means which, as shown in Fig. 1, comprises a cam operated switch 4I] and an indexing relay 4I arranged to control the `signal frequency supplied by a suitable'oscillator 42. For purposes of illustration, the oscillator is indicated as being capable of generating a cycle signaling frequency. As shown, the cam operated switch 40 includes a pair of contacts 43 arranged to control the energizing winding of the indexing relay 4I and an operating cam 44 which is carried by the post I3 so as to close the contacts 43 at a predetermined point during each revolution of the antenna structure. The indexing relay 4I is provided with two pairs of contacts 45 and 45, the contacts 45 being connected to control the oscillator 42 and the contacts 46 forming a part of suitable cardioid .control means, indicated by the reference numeral 41,' which will be more fully described hereinafter.

In addition to the above referred to elements, the field Istation equipment shown in Fig. 1 includes a suitable selector switch 48 for selectively controlling the switches 3| to 34,1inclusive, a lockout relay 48a, and suitable selector control means 49, which control means 49 is illustrated in detail in Fig. 3 and will be more fully described hereinafter. As Isho-wn, the selector switch 48, the lockout relay 48a, and the output side of the detector and audio amplifier 33 are directly connected to one end of the transmission line 39, While the selector control means 49 and the E25 cycle oscillator are connected to the transmission line through the contacts of the lockout relay. While the single transmission line 39 may, of course, comprise two conductors, one conductor is all that is necessary, the return circuits being effected through the usual ground connections as indicated in the drawings.

At the control station, which is shown in Fig. 2, the transmission line 39 i-s connected to a second audio amplifier 5I, and the output of this audio amplier is connected to a plurality of suitable filter units 52, 53, 54, and 55. The filter unit 52 is a high pass filter unit, preferably capable of passing frequencies of 300 cycles and above, and is provided in order to insure the removal from this branch of the incoming circuits of all of the relatively low signaling and control frequencies. As shown, the filter units 53 and 54 are connected to the output of the lter unit 52, the iilter unit 53 being adapted to reject the constant beat note frequency supplied to the transmission line by the audio amplifier 33. Thus the output or this filter 53 contains all of the audio components above 399 cycles except a small spectrum around 1G20 cycles, and accordingly any voice frequencies present in a modulated carrier picked up by the antenna structure are transmitted through this filter unit 53 to a suitable loud speaker 55 which comprises a monitor channel. By means of this monitor channel the operator is able to identify the var ious signals received and may listen for directional bearing requests.

The band pass filter 5d is a highly selective nlter adapted to pass frequencies having only a plus orv minus variation of approximately 30 cycles f fromY the beat note VVfrequency suppiiedby Vthe radio receivers to thetransmission line. The high order of selectivity employed in this filter, which is preferably a 1020 cycle unit, enables the removal of substantially all static interference side bands. It has been found that even under severe static conditions, the beat note present at the output terminal of the filter 5i is substantially pure, and of course` this beat note is present only when a carrier frequency is being received at the antenna station.

The band pass filter 55, which is connected in parallel with the filter unit 52, is adapted to pass the 120 cycle signal frequency placed on the transmission line by the oscillator 4Z, and it Will thus be seen that the frequencies passing over the transmission line from the antenna site are separated into three distinct channels, one of which constitutes a 120 cycle indexing channel, the second of which constitutes a 1020 cycle directional signal channel, and the third of Which constitutes an audio monitor channel.

In order that a continuous record of the signal intensity received at the antenna station and transmitted over the transmission line 3S may be produced at the control station of Fig. 2, recording means of the type disclosed in our above referred to copending application are provided at the control station. In Fig. 2 the recording means is shown as comprising a rotatable drum or recording surface 5i adapted to be driven through suitable reduction gearing (not shown) by a rnctor 58, the energization of which is controlled. by a suitable motor starting switch 5d. The motor for the` recording means and the motor for the antenna structure are preferably of the synchronous type, and are energized from suitable 60 cycle sources of energy so that the recording drum 51 will be rotated in synchronism with the rotati ing antenna structure.

Associated with the recording drum is a tracing element or pen 5B adapted to be energized through a suitable rectifier 6l from the 1020 cycle channel containing the band pass iilter 54, the recording pen 5S being preferably of the DArsonval type shown in our copending application, so that the pen, when energized, will trace on the recording surface '5'1 a continuous record of the signal intensity.

Also associated with the recording surface or drum 51 is an indexing pen or tracing element 62 adapted to be actuated by an energizing magnet E3 connected for energization through a suitable rectifier 6d from the 120 cycle signaling 5' channel containing the band pass lter 55. Also energized from this 120 cycle channel is a suitable signal light E5 for indicating when the loops of the antenna structure are rotating, and a suitable control relay 66 which co-operates with the starting switch 59 to control the energization of the recorder motor 58. In addition to the above described equipment, the control station shown in Fig. 2 includes a plurality of signal transmitting means 6l, 68, and S9 adapted to be energized from a suitable source of 60 cycle energy, the transmitting means 68 and S9 being connected, as shown, to a suitable voltage divider` 'l0 whereby the signal energy imposed on the transmission line by the devices 68 and` 69 is at a reduced voltage comprising only a fraction of the signal energy voltage impressed by the device 61. All of the devices 6l, E8v and E9 are connected by means of a conductor il to the transmission line 39.

The transmitting means S1 is of the type adaptto impress on a signaling circuit a's'elected number of short impulses for controlling the selector switch d-8, the number of impulses determining tlie operation of the selector switch, and this transmitting means may constitute an ordinary telephone dial. The transmitting device -68 constitutes a push-button controlled pulsing relay arrangement adapted, when the push button is operated, to transmit a single pulse of predetermined duration. Such devices are of course Well known in the art, and accordingly the details of the pulsing relay means have not been illustrated. The third transmitting device comprises merely a manually operable double-pole singlethrow switch adapted to be opened and closed, as desired, to impose on the signaling circuit a continuous 60 cycle signaling current and also to effect energization of the starting switch 59 for the record-er motor 58.

With the above description of the component parte of the apparatus constituting the field station of Fig, l and the control station of Fig. 2, it is thought that a complete understanding of our invention may now be had from a description of the operation required to obtain a bearing on any selected transmitting station. as, for example, a transmitter carried by an airplane in flight, the bearing of which, with reference to the iield station, it is desired to determine.

The first control operation, in order to put the direction finder in condition for recording a bearing, is to start the loop rotating motor at the field station This may be accomplished simply by pressing the push button of the transmitting device B8 so as to impress on the transmission line 39, through the conductor 1i. a measured pulse of 60 cycle energy at the previously referred to reduced voltage Which is preferably less than one-half the full line voltage of the 60 cycle source and may be as low as two volts. The device 68 is so arranged that the pulse will be of a duration on the order of magnitude of one-tenth of a second, regardless of the length of time that the push button is held in its depressed position.

At the field station end of the transmission line 39, this pulse of low voltage 60 cycle energy is transmitted through conductors l2 and 13, the contacts of the lockout relay 48a, and a conductor 13a to the selector control means 49, the

9 8| of the relay 00 after this latter relay has operated.

The above-described application of power to the cardioid control means 41 conditions this control means 41 for operation by the contacts 49 of the indexing relay 4| under the control of the cam switch 50 carried by the rotating antenna structure. The details of the cardioid control means, which are fully described and claimed in our above-identified copending application, are shown in Fig. 4 and it will be seen that closure of the contacts 45 completes an energizing circuit for a control relay |06 having an energizing winding |51, two pairs of normally open contacts |08 and |09, respectively, and a pair of normally closed contacts H0. This circuit may be traced from the positive side of the source of energy represented by the conductors 90, through the conductors |H, H2, H3, and H4, the relay contacts 46, the conductor H5, the relay winding |01, and by Way of a conductor H9 to the negative side of the source of energy. In order to simplify the drawings, the return connection to the negative side of the source of energy represented by the conductors 90 is not shown in full, but is indicated merely by a conventional minus sign.

.in addition to the control relay |05, the cardioid control means 41 includes a plurality of control relays H1, H8, and H9, the energizing winding |20 of the relay H9 being connected in the output circuit of a full Wave rectifier |2| having a pair of plates or anodes |22, a pair of cathodes |23, and a pair of control elements or grids |24. As shown, the grids or control elements |24 are adapted to be energized from a secondary Winding |25 of a suitable coupling transformer', the primary Winding |25 of which is connected by the conductors to a suitable antenna for energization by the carriers of the transmitting stations to which the radio receivers are tuned. The primary winding |26 is preferably connected to the system of Fig. l at any suitable point so that it will be energized regardless of the one of the receivers 21 to 30, inclusive, which is selected and in operation, or the primary Winding may, if desired, be connected to an entirely separate antenna and receiver. Inorder to provide a constant negative bias on the control elements |24 of the reCtif er tube |2|, the midpoint of the secondary Winding |25 is connected to the negative side of the source of energy, as shown, and the cathodes I 29 are connected to a suitable potentiometer represented as comprising resistance elements |21 connected across the direct current source of energy represented by the conductors 90.

Whenever carrier energy is being supplied to the rectier tube through the transformer, current will flow through the winding |20 of the control relay H19 by Way of a circuit which eX- tends from the positive one of the conductors 90, through a conductor |28, the Winding |20, the conductor |29, the anodes |22, the cathodesV |23, and by Way of a conductor |30 to the movable contact I3! on the potentiometer comprising the resistance elements |21.

As previously described, the operating motors of the antenna arrangement having been energiaed, the cam switch 40 operates to energize the indexing relay 4| and eilect intermittent opening and closing of the contacts 46, and in describing the operation of the cardioid control means 41 it will be assumed that a carrier is being supplied to the Winding |26 of the transformer so as. to eiect operation of the relay H9. Upon closure of the contacts |52 of the relay H9, a condenser |33 will be discharged to effect energization of the relay H5, the condenser having previously been charged through a circuit which may be traced from the positive one of the conductors 90, through the conducto-1' |25, a resistor |34, a conductor |35, and the condenser |33 to the negative one ofthe conductors by Way of a conductor |35. The energizing circuit for the relay H8, established by closure of the contacts |32, may bev traced from one side of the condenser |33, through the conductor |35, the contacts |32, a conductor |31, the winding |38 of the relay H9, a conductor |39, the contacts |08 on the relay which, as previously described, has been operated by closure of the contacts 49 on the indexing relay and by Way of the conductor H6 to the negative one of the conductors to which the opposite side of the condenser |33 isV also` connected by way of the conductor |36.

Following initial energization thereof, the relay H8 is-held in its operated position by a holding circuit which may be traced from the positive one of the conductors 90, through the conductors IH, H2, and |40, contacts |09, conductor |4|, contacts |42 on the relay H 8, conductor |43, the Winiding |38 0f the relay H8, conductor |39, contacts |08 and by Way of the conductor H6 to the negative one of the conductors 90.

Closure of the contacts |44 of the relay H8 establishes an energizing circuit for the Winding |45 of the relay H1, which circuit may be traced from the positive one of the conductors 90,

through the conductors |H and |45, the contacts |44, conductors |41 and |43, and by Way of the winding |45 and a conductor |49 to the negative one of the conductors 90. The relay H1 is thus operated and the energizing circuits thus far traced continue to exist until the circuit is broken at the contacts 46 of the indexing relay, at which time the relay |05 is deenergized allowing contacts |08 and |09 to open and contacts H0 to close. Opening of the contacts |09 interrupts the previously traced holding circuit for the relay H8, and the consequent opening of the contacts |44 on this relay in turn interrupts the energizing circuit for the relay H1. Simultaneously, however, closure of the contacts H0 o-n the relay |05 provides a self-holding circuit for the relay |1 which may be traced from the positive one of the conductors 90 through the conductors IH, H2, and |49, contacts H0, a conductor |50, contacts |5| on the relay H1, conductors |52 and |48, and by Way of the Winding |45 and the conductor |49 to the negative one of the conductors `90. This transfer of the holding circuit for the relay H1 is accomplished Without affecting the operated condition of the relay because this relay is of the sloW-to-release type, as indicated diagrammatically in Fig. 4 by the usual copper slug |53a.

Operation of the relay H1 of course causes closure of the relay contacts |53, thereby completing an energizing circuit for the cardioid relay i5 which may beY traced from the positive one of the conductors 90, through the conductors HI, H2; H3, and |54, the contacts |53 and by Way of a conductor |55 to the operating Winding of the relay IB, the opposite side of which is connected to the negative side of the sotu'ce of energy as indicated by the ground connection shown in Fig. 1. As previously described, energization of the relay I6 is eiective to connect the loops l and II in additive parallel relation with each other to the conductors 2'5, and to connect the vertical antenna I4 to the conductor orbus bar 2%. Thus during the rst revolution of the lantenna structure, the loop antennas and thevertical antenna will be connected in circuit so as to produce a directional or cardioid pattern which, as will beV hereinafter described, is recorded on the recording surface 5T by the tracing element G.

The previously described connections exist until the contacts 4B of the indexing relay 4| are again closed upon completion of one revolution of the antenna structure, whereupon the relay |03 -will again be energized through the previously traced energizing circ-uit, causing the contacts lIU to open and interrupt the previously traced self-holding Vcircuit for theY relay II'I. The capacity of the condenser |33 and the ohmic resistance of the resistor |34 are so chosen that between successive closures of the contacts 46 of the indexing relay 4| there will elapse an insufcient time to permit the accumulation yon the Acondenser |33 of a charge of sulicient magnitude to eect operation of the relay H8. Therefore, even though the initial energizing circuit Vfor the relay H8 is completed through the contacts of the relay ISS when this relay is again operated, the relay I|8 will not operate and accordingly the relay |Il opens, thereby interrupting at contacts |53 the energizing circuit for the cardioid relay I6. Thus the relay I5 will return to the deenergized position shown in Fig. 1 and the loops I@ and II are connected in opposed parallel relation to the conductors or bus bars 25,V as heretofore described. Due to the-fact that the capacity and resistance values of ,the condenser |33 and the resistor |34 are chosenl as indicated above, the operating cycle cannot be repeated until a sufficient time has elapsed to permit the condenser |33 torattain a new charge of sufficient magnitude to operate therelay |32.

After the desired record has been made in a manner toV be further described hereinafter and the system has been allowed to rest for a relatively short time, operating voltage will build up across the condenser |33 and the above described cycle of operations may be repeated. Such an operating voltage, however, will not build up across the condenser until the system is thus allowed to rest because of the fact that the condenser is discharged each time that the contacts |08 of the relay |06 close.

It -will now be apparent that as soon as energy is applied to the cardioid control, as'heretofore described, the cardioid relay IB is operated by the rst closure of the cam switch and remains closed until the next revolution of the antenna structure causes the energizing circuit for the relay i6 to be broken. The relay I6, therefore, returns to its deenergized position so as to connect the loops l0 and I| in opposed parallel circuit relation and disconnect the vertical antenna Ill, and the relay I6 will remain in this position during subsequent revolutions of the antenna structure. Furthermore, the carrier controlled interlock relay |93 which is energized through the conductors |09 insures that the above-described cycle of operations will take place -only when a carrier is being received by the antenna structure. Y

\ Closure of the transmitting means or switch 69 to .impose the above referred to continuous low voltage signaling current on the transmission line l2V -39 is also effective through the lower pole thereof to prepare an energizing circuit for thejrecorder motor 53, so that the recorder motor willsbegin to operate as soon as a cycle pulse is received over the transmissionline. As shown in Fig. 2, this energizing circuit extends from the source of 60 cycle energy and the voltage divider 10, through the lower pole of the switch 69 andthe conductor 3| 'to Ythe energizing Winding of. the

motor starting switch 59, and from thisenergizing winding the circuit is completed by the conductor 92 and the contacts of the relay 65B to the Vground connection 93. Thus, as` soonas the relay 66 closes, the motor starting switch 53 will be energized to close its contacts gland 95 and connect the motor 38 to its source of energy. Closure of the motor starting switch ,59 also is effective through the contacts B thereof to establish a self-sealingcircuit,v so that the motor starting switch 59 remains energized after the relay 66 has opened and the motor 58 will therefore continue to operate until the switch 69 is manually opened after the bearing reading has been taken.

It Ywill now be clearr that, through the abovedescribed cycle of control operations, the particular station on which a bearing is to be taken has been selected, the antenna structure has been started to rotate, and the recorder motor has been energized to drive the recording surfacein syn-V chronism with the rotating antenna structure. Therefore, there willbe imposed on the eld Vstation end of the transmission line 39 a 1020 Y cycle note which varies in intensity in accordance with the directional characteristics of the radio wave picked up by the antenna structure. This 1020 cycle note passes through the amplier 5|, the filter units 52 and V54, and the rectier 6I to the tracing element 60 which records on the recording surface 51 a traceof the signal intensity. At the same time, there is transmitted over the transmission line 39 a 120 cycle pulse of signal energy whichl causes the indexing pen or tracing element 62 -to record on the chart a reference mark each time that the antenna structure passes through a predetermined compass position.

During the rst revolution of the recorder, the conventional cardioidl pattern will be traced thereon by the tracing element 60 in order to indicate the general sense or direction of the transmitting station, and on each succeeding revolution of the recording surface the tracing element 6) will impart to the recording surface a continuous trace of the 1020 cycle signal received with the loops I and II connected in opposed parallel circuit relation. The pen will of course retrace this path during successive revolutions if there hasV been no change in the signal intensity for identical positions of the antenna system. Variations in the propagating medium or in the signal energy received due to other disturbances will ofcourse appear in the trace made by the pen 66, except in so far as they are eliminated by the antenna structure and its associated apparatus, and accordingly an average trace may readily be determined from the record produced.

Y The recording paper, or similar recording surface which is wrapped around the drum 58, may be graduated in degrees and, accordingly,vthe compass position of any maximum or minimum point in the continuous trace of the signal energy may readily be located by reference to the indexing mark formed on the recording paper or surface by the indexing pen or tracing element 62. The direction finder is preferably allowed to operate for a period of thirty secondsto one minute,

so that from seven to fifteen. bearings will be obtained, the antenna structure preferably being rotated at a speed-of approximately fifteen revolutions per minute, and the direction nder malf then be shut down. To stop the recorder motor i! in order to enable removal of the record paper from the recording surface 5l, it is necessary only to open the switch 69 so as to interrupt the previously traced holding circuit for the motor starting switch 5S. rIhe operator may then remove thevrecord paper and measure the distance from the index mark to the bearing null which is nearest tothe cardioid bearing. rllhis distance indicates in degrees the bearing of the transmitting-stationon which the bearing'. has been taken.

Upon opening of the switch S8, the relay 1li of theselector control means immediately returns toits deenergised position and opens. the energizing circuit to the slow-to-release relay 17. The relay 'Il then opens and deenergizes the relay 8d which is also slow-to-release and therefore will not effect closurev of the contacts l for a short interval after opening of the contacts 1B on the relay 'il has occurred. The slow-to-release characteristics ofthe relay EQ insure that all of the relaysfhl, l1, and dil willreturn to their respective deenergized positions without completing an energizing circuit for the ratchet relay 83 through the contacts 75 73, and 3l.

In,` order to stop the rotation of the antenna structure, it is necessary only to actuate the push button of the pulsing relay means 53 so as to transmit a short 60 cycle pulse of low voltage to the selector control means t9 so as to cause the relays 14, Tl, and Sii to operate as hereinbefore described to energize ratchet relay S3. This energization causes the ratchet relay to move forward one step, whereupon the contacts of the ratchet relay open and interrupt the circuit to the antenna motor in the base I5. All of the parts having now returned to their initial positions, another bearing reading may be taken on any desired transmittingstation merely by following again the above described procedure.

While we have shown particular embodiments of our invention, it will be understood, of course, that we do not wish to be limited thereto since many modifications may be made, and we, therefore, contemplate by the appended claims to cover any such modiiications as fall within the true spirit and scope of our invention.

Having thus described our invention, what we claim and desire to secure b-y Letters Patent is:

1. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station, radio receiver means at Said antenna station including a plurality of channels respectively tuned to receive signals of diierent preselected frequencies picked up by said antenna means, means at said control station for selectively imposing on said transmission line control signals of a predetermined frequency having preselected characteristics, means at said antenna station responsive to said control signals for selectively connecting between said transmission line and said antenna means a selected one of said channels of said receiver means corresponding to the selected signal characteristic, heterodyning means associated with said receiver means for imposing` on said transmission line an output beat note of substantially constant frequency regardless of the selected receiver channel tuning, re-

Cording means Vat said control station energizable to produce a record trace reflecting the intensity of the energizing signal, and filter means between said recording means and said transmission line for rendering said recording means responsive only to signals of said constant beat frequency, whereby a bearing trace of the received signal energy may be produced from any of said differently tuned receiver channels.

2. In a radio direction finder system having anantenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station, radio receiver means at said antenna station including a plurality of channels respectively tuned toreceive signals of different preselected frequencies picked up by said antenna means, means at said control station for selectively imposing on said transmission line control signals of a predetermined frequency having preselected characteristics, means at said antenna station responsive to said control signals for selectively connecting between said transmission line and said antenna means a selected one of said channels of said receiver means corresponding to the selected signal characteristic, heterodyning means associated with said receiver means for imposing on said transmission line an output beat note of substantially constant frequency regardless of the selected receiver channel tuning, i11- dexing means at said antenna station for imposing on said transmission line indexing signals differing in frequency from said control signal frequency and said beat note frequency, said indexing signals reecting the compass position of said antenna means, recording means at Said control station having a plurality of energizable tracing elements, and filter means between said recording means and said transmission line for rendering one element of said recording means responsive only to said constant beat note frequency and another element thereof responsive only t0 said indexing signal frequency, whereby bearing traces of the signal energy received from said antenna means may be produced at said control station regardless of the frequency of the received signal and oriented with the compass position of said antenna means.

3. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station, radio receiver means at said antenna station including a plurality of channels respectively tuned to receive voice modulated signals of different preselected carrier frequencies picked up by said antenna means, means at said control station for selectively imposing on said transmission line control signals of a predetermined frequency having preselected characteristics, means at said antenna station responsive to said control signals for selectively connecting between said transmission line and said antenna means a selected one of said channels of said receiver means corresponding to the selected signal characteristic, heterodyning means associated with said receiving means for imposing on said transmission line the voice frequencies of said signals and a beat note of substantially constant frequency regardless of the selected receiver channel tuning, loud-speaker means at said control station, recording means at said control station energizable to produce a record trace relter means connected to the control station end of said transmission line for rejecting from said loud-speaker said control signal and said beat note frequencies and for rendering said recording means responsive only to signals of said beat note frequency, whereby a monitor channel is provided and a bearing trace of the received signal energy may be produced from any of said differently tuned receiver channels.

4. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the combination o-f rotatable directional antenna means at said antenna station, radio receiver meansrat said antenna station including a plurality of channels respectively tuned to receive voice modulated signals of Ydifferent preselected carrierY frequencies picked up lby ksaid antenna means, means at said control station for selectively imposing on said transmission line control signals of a predetermined frequency having Apreselected characteristics, means at said antenna station responsive to said control signals for selectively connecting between s aid transmission line and said antenna means a selected one of said channels of said receiver means corresponding to the selected signal characteristic, heterodyning means associated with said receiver means for imposing on said transmission line the voice frequencies of said sigy nals and a beat note f substantially constant frequency regardless of the selected receiver channel tuning, indexing means at said antenna station for imposing on said transmission line index' ing signals differing in frequency from said control signal frequency and said beat note frequency, said indexing signals reflecting the compass position of said antenna means, recording means atsaid control station having a plurality'of energizable tracing elements, monitor means at said control station responsive to voice frequencies, and filter means connected to the control station end of said transmission line for rejecting from said monitor means said indexing, signal and beat note frequencies, for rendering one element of said recording means responsive only to said beat note frequency and for rendering another element thereof responsive only to said indexing signal frequency, whereby signals picked up by said antenna means may be monitored and bearing traces of the signal energy received from said antenna means may be produced at said control station regardless of the frequency of the received signal and oriented with the compass position of said antenna means.

5. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station, radio receiver means at said antenna station including a plurality of channels respectively tuned to receive signals of different preselected frequencies picked up by said antenna means, means at said control station for selectively imposing on said transmission line control signals of a predetermined frequency having preselected characteristics, means at said antenna station responsive to said control signals for selectively connecting between said transmission line and said antenna means constant frequency'regardless of the selected re- Y ceiver channel tuning, motor means at said antenna station for rotating said antenna means,

means at said control station for imposing on said transmission line a second signal of the same control frequency but of different character than said signals of preselected characteristics,.means at said antenna station responsive to said second control signal for energizing said motor means, indexing means for imposing on the antenna station end of said transmission line indexing sigals differing in frequency from said control signal frequency and said beat note frequency and refleeting the compass position of said antenna means, recording means at said control station having a movable recording surface and a plurality of tracing elements, filter means at said control station for rendering one tracing element responsive only to said constant beat note frequency and another tracing element responsive only to said indexing signals, and means initially rendered effective by an indexing signal for driving said recording surface in synchronism with the rotation of said antenna means to produce at said control station a bearing trace of the signal energy received from said antenna means oriented with the compass position thereof` regardless of the frequency of the received signal.

6. In a radio direction finder system having an antenna station and a remotely located control station connectedby a transmission line, the combination of rotatable directional antenna means at said antenna station including a plurality of antenna elements adapted to be selectively connected in different circuit relations with eachv other, receiver means at said antenna station having an output circuit connected to said transmission line, indexing signal means controlled by rotation of said antenna for imposing on the antenna end of said transmission line signals of predetermined signal frequency, motor means for rotating said antenna, a plurality of control means at said antenna station for controlling said antenna circuit connections, for connecting said receiver means to said antenna means and for controlling said motor means, a source of signal frequency at said control station, signal means at said control station for selectively connecting said source to said transmission line to impose thereon signals of different characteristics separately to effect operation of said antenna control means, said receiver control means and said motor control means at said antenna station, and means at said control station jointly controlled by said indexing means and said Yreceiver means at said antenna station and by said signal means at said control station for determining the compass bearing of radio frequency signals picked up by said antenna meansV during rotation thereof.

7. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station including a plurality of antenna elements adapted to be selectively connected in different circuit relations with each other, receiver means at said antenna station having an output circuit connected to said transmission line, indexing signal means controlled by rotation of said antenna for imposing on the antenna end of said transmission line signals of predetermined signal frequency, motor means for rotating said antenna, a plurality of control means at said antenna station for controlling said antenna circuit connections, for connecting said frequency at said control station, signal means at said control station for selectively connecting said source to said transmission line to impose thereon signals of different characteristics separately to effect operation of said antenna control means, said receiver control means and said motor control means at said antenna station, filter means at said control station for dividing into separate channels said indexing signal frequency and the output signal frequency of said receiver means transmitted over said transmission line and for rejecting from said channels the signal frequency of said source at said control station, and means at said control station energizable by said output signal frequency and said indexing signal frequency for recording a bearing trace of said output signal frequency during rotation of said antenna means and orienting said trace relative to the compass position of said antenna means.

8. In a radio direction finder system having an antenna station and a remotely located control station connected by a transmission line, the cornbination of rotatable directional antenna means at said antenna station including -a plurality of antenna elements adapted to be selectively connected in diierent circuit relations with each other, receiver means at said antenna station having an output circuit connected to said transmission line for imposing thereon voice frequenf cies including a substantially constant beat note frequency, indexing signal means controlled by rotation of said antenna for imposing on the antenna end of said transmission line signals of predetermined frequency, motor means for rotating said antenna, a plurality of control means at said antenna station for controlling said antenna circuit connections, for connecting said receiver means to said antenna means and for controlling said motor means, a source of signal frequency at said control station, signal means at said control station for selectively connecting said source to said transmission line to impose thereon signals of different characteristics separately to eect operation of said antenna control means, said receiver control means and said motor control means at said antenna station, filter means at said control station for dividing into separate channels said indexing signal frequency, the output beat note frequency of said receiver means and the voice frequencies transmitted over said transmission line and for rejecting from said channels the signal frequency of said source at said control station, monitor means connected to one of said channels for receiving said voice frequencies, and means :at said control station energizable from said output beat not@ frequency channel and said indexing signal frequency channel for recording a bearing trace of said output signal frequency during rotation of said antenna means and orienting said trace relative to the compass position of said antenna means.

9. In a radio direction nder system having an antenna station and a remotely located control station connected by a transmission line, the combination of rotatable directional antenna means at said antenna station including a plurality of antenna elements adapted to be selectively connected in different circuit relations With each other, receiver means at said antenna station having an output circuit connected to said transmission line, indexing signal means controlled by rotation of said antenna for imposing on the antenna end of said transmission line signals of predetermined signal frequency, motor means for rotating said antenna, a plurality of control means at said antenna station for controlling said antenna circuit connections, for connecting said receiver means to said antenna means and for controlling said motor means, a source of signal frequency at said control station, signal means at said control station for selectively connecting said source to said transmission line to impose thereon signals of different characteristics separately to eiTect operation of said antenna control means, said receiver control means and said motor control means at said antenna station, recording means at said control station having a, movable recording surface and a plurality of tracing elements, lter means at said control station for rendering one tracing element responsive only to the output signal frequency of said receiver and another tracing element responsive only to said indexing signal frequency, and means initially rendered effective by a signal of said indexing frequency for driving said recording surface in synchronism with the rotation of said antenna means to produce at said control station a bearing trace of said receiver output frequency during rotation of said antenna means and to orient said trace with the compass position of said antenna means.

PETER C. SANDRETTO. ELMER. P. BUCKTHAL. 

